Can a marriage contract successfully designate a property as not being the matrimonial home in Ontario?

No, not for the core matrimonial home protections. Spouses can use a marriage contract to address a great deal about how property is owned and divided between them, but the Family Law Act specifically makes any provision in a domestic contract that tries to limit the matrimonial home protections unenforceable, regardless of how clearly the contract states it. In practice, this means a clause attempting to declare that a property the couple actually occupies as their family residence simply isn't a matrimonial home for legal purposes won't be effective to strip away those protections.

Whether a specific property is a matrimonial home ultimately turns on the facts — whether it's ordinarily occupied by the spouses as their family residence at the relevant time — not on what a contract says it should be treated as. Couples can still address plenty of other property matters in a marriage contract, including how a home's value is shared on separation, but the underlying consent-to-sell and possession protections tied to matrimonial home status generally can't be contracted away this directly. Anyone drafting or relying on a marriage contract with this kind of provision should get legal advice, since assuming the clause works as written can lead to real surprises later.